Multimodal neuroprotection induced by PACAP38 in oxygen-glucose deprivation and middle cerebral artery occlusion stroke models.

Pituitary adenylate cyclase activating peptide (PACAP), a potent neuropeptide which crosses the blood-brain barrier, is known to provide neuroprotection in rat stroke models of middle cerebral artery occlusion (MCAO) by mechanism(s) which deserve clarification. We confirmed that following i.v. injection of 30 ng/kg of PACAP38 in rats exposed to 2 h of MCAO focal cerebral ischemia and 48 h reoxygenation, 50 % neuroprotection was measured by reduced caspase-3 activity and volume of cerebral infarction. Similar neuroprotective effects were measured upon PACAP38 treatment of oxygen-glucose deprivation and reoxygenation of brain cortical neurons. The neuroprotection was temporally associated with increased expression of brain-derived neurotrophic factor, phosphorylation of its receptor-tropomyosin-related kinase receptor type B (trkB), activation of phosphoinositide 3-kinase and Akt, and reduction of extracellular signal-regulated kinases 1/2 phosphorylation. PACAP38 increased expression of neuronal markers beta-tubulin III, microtubule-associated protein-2, and growth-associated protein-43. PACAP38 induced stimulation of Rac and suppression of Rho GTPase activities. PACAP38 downregulated the nerve growth factor receptor (p75(NTR)) and associated Nogo-(Neurite outgrowth-A) receptor. Collectively, these in vitro and in vivo results propose that PACAP exhibits neuroprotective effects in cerebral ischemia by three mechanisms: a direct one, mediated by PACAP receptors, and two indirect, induced by neurotrophin release, activation of the trkB receptors and attenuation of neuronal growth inhibitory signaling molecules p75(NTR) and Nogo receptor.

Neuroprotective effect of endogenous pituitary adenylate cyclase-activating polypeptide on spinal cord injury.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuroprotective peptide expressed in the central nervous system. To date, changes in the expression and effect of endogenous PACAP have not been clarified with respect to spinal cord injury (SCI). The aim of this study was to elucidate the expression pattern and function of endogenous PACAP on the contusion model of SCI using heterozygous PACAP knockout (PACAP(+/-)) and wild-type mice. Real-time polymerase chain reaction methods revealed that the level of PACAP mRNA increased gradually for 14 days after SCI and that PAC1R mRNA levels also increased for 7 days compared with intact control mice. PACAP and PAC1R immunoreactivities colabeled with a neuronal marker in the intact spinal cord. Seven days after SCI, PAC1R immunoreactivity was additionally co-expressed with an astrocyte marker. Wild-type mice gradually recovered motor function after 14 days, but PACAP(+/-) mice showed significantly impaired recovery from 3 days compared with wild-type mice. The injury volume at day 7 in PACAP(+/-) mice, and the number of single-stranded DNA-immunopositive cells as a marker of neuronal cell death at day 3 were significantly higher than values measured in wild-type mice. These data suggest that endogenous PACAP is upregulated by SCI and has a neuroprotective effect on the damaged spinal cord.